The present invention relates to the irradiating arts. It particularly relates to radiation treatment of a subject using spatially intensity-modulated radiation to deliver targeted and controlled dosage distributions, and will be described with particular reference thereto. However, the invention will also find application in conjunction with controlled delivery of radiation for other applications such as diagnostic imaging as well as in other radiation absorption analyses such as computation of light absorption for optical modeling.
Oncological radiation therapy (sometimes called radiotherapy) is used for controlling, reversing, or sometimes even eliminating cancerous growths. Ionizing radiation such as high energy photons (e.g., x-rays or gamma rays), proton or neutron particles, or the like are applied to a cancerous tumor or other cancerous region. The ionizing radiation damages cellular DNA which can kill irradiated cells. Because growing and rapidly multiplying cancer cells are typically more readily damaged by the radiation and less able to repair such damage than are healthy cells, there is usually a beneficially built-in selectivity favoring elimination of cancerous tissue and survival of healthy tissue.
However, irradiated healthy tissue is usually also damaged by the radiotherapy to at least some extent, and such radiation damage can produce highly detrimental side-effects to the therapy which are preferably minimized or avoided. To reduce damage to healthy tissue, radiotherapy typically includes a series of treatments performed over an extended period of time e.g., over several weeks. Serial treatment facilitates beneficial repair of damaged non-cancerous cells between treatments.
Another approach for maximizing the beneficial cancer-killing effect of radiotherapy while minimizing damage to healthy cells is intensity modulated radiotherapy (IMRT). The IMRT technique employs a plurality of radiation beams applied to the target area simultaneously or sequentially at several angles or orientations. The spatial beam intensity profile is controlled using multi-leaf collimators or other beam-shaping elements known to the art, such that the cumulative dosage delivered to the target area is controlled to produce a selected radiation dosage profile that targets cancerous regions or tumors while minimizing the radiation dosage to neighboring critical structures.
A variation on the IMRT method is tomotherapy. This method uses a geometry similar to that of helical computed tomography (CT). A linear electron accelerator, or linac, is mounted on a rotating gantry that rotates the beam aperture about the subject while linearly moving the subject in a direction perpendicular to the plane of source rotation. This effectuates a helical orbit of the beam aperture about the subject. During helical orbiting, the beam is selectively controlled to deliver a selected radiation dosage profile to the target area. Optionally, a tungsten or other target is inserted in the beam path, which intercepts the accelerated electrons and emits photons, e.g. x-rays or gamma rays, which irradiate the target area.
Determination of appropriate radiotherapy parameters for delivering a selected radiation dosage profile is a complex task. Usually, planning images of the target area are acquired using computed tomography (CT) or another diagnostic imaging technique. CT beneficially provides both structural information and radiation attenuation or tissue density information which is used in determining radiotherapy radiation absorption profiles. IMRT planning can include optimizing as many as ten thousand beam parameters, while planning for tomotherapy is even more complex due to the continuous helical orbit of the radiation aperture, and can include optimizing around sixty thousand parameters.
The present invention contemplates an improved apparatus and method which overcomes the aforementioned limitations and others.
According to one aspect of the invention, a method is provided for delivering to a subject a selected radiation treatment described by a treatment radiation dosage distribution objective. The delivering includes application of at least one intensity-modulated beam whose radiation output is described by a plurality of beamlet parameters. The beamlet parameters are divided into a plurality of groups, each group including one or more beamlet parameters. A group weighting is assigned to each group based at least on a fraction of the beamlet parameters included in the group. A first group is selected. A first intermediate radiation dosage distribution objective is computed based on the treatment radiation dosage distribution objective and the first group weighting. The first group of beamlet parameters is optimized respective to the first intermediate radiation dosage distribution objective. A next group is selected. A second intermediate radiation dosage distribution objective is determined based on the treatment radiation dosage distribution objective and the next group weighting. The next group of beamlet parameters is optimized respective to the second intermediate radiation dosage distribution objective. The next group selection, second intermediate objective determination, and next group optimization steps are repeated to optimize all the beamlet intensity parameters. The optimized beamlet intensity parameters are converted to a deliverable sequence of radiation fields. Then at least one intensity-modulated beam is applied to effectuate the deliverable sequence.
According to another aspect of the invention, a radiation treatment apparatus is disclosed for delivering a radiation treatment to a subject. A diagnostic imaging scanner acquires a diagnostic image of a target area of the subject. A contouring processor computes a radiation treatment objective based on the diagnostic image. A radiation delivery apparatus is configured to deliver the radiation treatment objective to the subject. The radiation produced by the radiation delivery apparatus during the radiation treatment is representable as a plurality of parameterized beamlets. An inverse planning processor computes beamlet parameters conforming with the radiation treatment objective. The inverse planning processor performs a method including: grouping the beamlet parameters into a plurality of groups each including one or more beamlet parameters; assigning a contribution weight to each beamlet parameter group; optimizing a first beamlet parameter group with respect to a first intermediate target dosage objective corresponding to the radiation treatment objective weighted by the contribution weight of the first beamlet parameter group; and optimizing successive beamlet parameter groups with respect to a second intermediate target dosage objective weighted by at least the contribution weight of at least the currently optimized beamlet parameter group. A conversion processor converts the optimized beamlet parameters into configuration parameters of the radiation delivery apparatus.
According to yet another aspect of the invention, an apparatus is disclosed for delivering to a subject a selected radiation treatment described by a treatment radiation dosage distribution objective. The delivering includes application of at least one intensity-modulated beam whose radiation output is described by a plurality of beamlet parameters. A grouping means is provided for dividing the beamlet parameters into a plurality of groups, each group including one or more beamlet parameters. A weighting means is provided for assigning a group weighting for each group based at least on a fraction of the beamlet parameters included in the group. A means is provided for computing an intermediate radiation dosage distribution objective based on the treatment radiation dosage distribution objective and combined weightings of one or more selected groups. An optimizing means is provided for optimizing the beamlet parameters of a current group respective to the intermediate radiation dosage distribution objective. A looping means is provided for successively applying the means for computing an intermediate radiation dosage distribution objective and the optimizing means to determine optimized values for the beamlet parameters of each group. A converting means is provided for converting the optimized beamlet intensity parameters to a deliverable sequence of radiation fields. A radiation delivery means is provided for applying at least one intensity-modulated beam to effectuate the deliverable sequence.
One advantage of the present invention resides in improved speed in computing parameters for delivering a selected radiation treatment objective.
Another advantage of the present invention resides in reduced computational load during radiation treatment planning.
Yet another advantage of the present invention resides in substantially reducing the complexity of parameter optimization processing in tomotherapy planning.
Numerous additional advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment.